The present invention relates to a method for preparing a pigment composition, more particularly, to a novel method for preparing a pigment composition containing pigment highly concentrated and thoroughly-dispersed, in the form of fine particles, in a vehicle.
Pigments are used in various coloring materials such as paints, printing inks, colorants for plastic and textile printing pastes. The degree of dispersion of the pigment in the vehicle considerably affects color tone, tinting strength, hiding power, clearness, transparency and physical properties and, therefore, it is necessary to thoroughly disperse the pigment in the form of fine particles in the coloring material. For this purpose, a pigment composition containing, in a high concentration, a thoroughly-dispersed pigment in the form of fine particles is conventionally prepared in advance and such a concentrate is then used to form various coloring materials.
Conventional methods for preparing pigment compositions include (1) a method of milling pigment and its dispersing media (resin, plasticizer, solvent, etc.) by means of a 2-roller mill and (2) a method in which a pressed cake of pigment, solvent and vehicles is kneaded together and during such rolling or kneading operation, the pigment is transferred to the vehicles and distributed therein. However, such conventional methods are accompanied by various drawbacks. Method (1) is not only uneconomical as it requires enormous energy and time to disperse pigment but also it creates unfavorable working conditions as pigment is scattered and solvent is evaporated into the workshop atmosphere. On the other hand, method (2) is incapable of providing a sufficient degree of dispersion and thus requires an additional dispersion step involving a dispersing apparatus such as a 3-roller mill. Method (2) also requires a cumbersome post-treatment of waste water which contains surfactant or solvent generally added as a flashing agent.